Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original paper

Jakub Plášil, Radek Škoda, Anthony R. Kampf, Ivan Němec, Nicolas Meisser, Georges Favreau

Crystal structure of synthetic “magnesiorietveldite”, Raman spectroscopy data and bond-valence approach to the svornostite group of minerals

Journal of Geosciences, volume 70 (2025), issue 3, 163 - 176

DOI: http://doi.org/10.3190/jgeosci.0047.25

The new synthetic counterpart of a potentially new member of the svornostite group of minerals, “magnesiorietveldite”, ideally Mg(UO₂)(SO₄)₂(H₂O)₅, is orthorhombic, space group Pmn2₁, a = 12.7950(9), b = 8.3288(4), c = 11.2962(4) Å, V = 1203.80(11) ų and Z = 2. The crystal structure (R₁ = 0.0168 for 3113 I > 3σI reflections) contains uranyl-sulfate chains that are linked into sheets by M1O₂(H₂O)₄ and M2O₂(H₂O)₄ octahedra, where Mg is a dominant cation over Zn at both sites. The structure is well known and has already been described for other members of the svornostite group; the fundamental building unit - an infinite [(UO₂)(SO₄)₂(H₂O)]^2- chain is common in several uranyl minerals and synthetic compounds. Synthetic “magnesiorietveldite” was obtained after treatment of a specimen containing pitchblende with sulfuric acid. Electron microprobe analyses yielded the empirical formula (Mg_0.63Zn_0.22Cu_0.09Fe_0.05)_∑0.99(UO₂)(SO₄)₂·5H₂O, confirming the predominance of Mg over the other divalent cations. Infrared and Raman spectroscopy confirmed the presence of structurally non-equivalent molecular H₂O and sulfate tetrahedra. We append an extensive discussion on the role of molecular H₂O in the svornostite-group of minerals based on the bond-valence approach.